As a wireless transmitter receiver for a vehicle, a slim card key, which can be accommodated in a wallet, has been conventionally proposed. In response to an inquiry signal from an on-board device, the card key transmits an ID code to the on-board device, and permits lock or unlock of a vehicle door or permits to start an engine on condition that the ID code is authenticated.
As described in a patent literature 1, for example, a card key includes a card key body and a cell cover. The card key body has a cell accommodation portion to accommodate a cell as a drive source (for example, a button cell) therein to be replaceable. The cell cover closes the cell accommodation portion.
As structures of the cell cover, there are a structure as shown in FIGS. 14A and 14B and a structure as shown in FIGS. 15A and 15B. In the structure shown in shown FIGS. 14A and 14B, a cell cover 110 has an insertion projection portion 111. The insertion projection portion 111 of the cell cover 110 is inserted into a cell accommodation portion 101 of a card key body 100 to cover the cell accommodation portion 101. In the structure shown in FIGS. 15A and 15B, a cell cover 210 has a substantially U-shape in cross-section. The cell cover 210 is fixed to a card key body 200 to cover an opening 202 of a cell accommodation portion 201, thereby to close the cell accommodation portion 201.
In a fixing structure of the cell cover 110 shown in FIGS. 14A and 14B, the cell cover 110 is fixed to the card key body 100 by engaging engagement projections 112 of the cell cover 110 with engagement recesses of the card key body 100. The engagement projections 112 have a triangular shape and are disposed at opposite side surfaces of the insertion projection portion 111. The engagement recesses 102 have a triangular shape in cross section and are provided on opposite inner side walls of the cell accommodation portion 101. In a fixing structure of the cell cover 210 shown in FIGS. 15A to 15C, the cell cover 210 is fixed to the card key body 200 by engaging engagement projections 212 of the cell cover 210 with engagement recesses 203 of the cell accommodation portion 201. The engagement projections 212 are provided to project from inner walls of up and down side portions 211 of the cell cover 210, which has the U-shape in cross-section. The engagement projections 212 have a trapezoidal shape in cross section. The engagement recesses 203 are provided at positions adjacent to the opening 202 of the cell accommodation portion 201, and have a trapezoidal shape in cross section. Sloped surfaces of the engagement projections 212 and the engagement recesses 203, which correspond to sloped sides of the trapezoidal shape, define a gently sloped angle to enable the cell cover 210 to be pulled out from the card key body 200 in a state of being pinched.
However, in the structure where the cell cover is fixed to the card key body by the engagement of such engagement projections and engagement recesses, if an engagement force is large, it is difficult to remove the cell cover. On the other hand, if the engagement force is small, the cell cover will be unexpectedly removed from the card key body by a shock, such as a shock caused when the card key is dropped or the like.